1. Field of the Invention
The present invention relates to a curing composition which is adapted to be coated onto the surfaces of plastic products, etc. and cured to protect the surfaces of the products. More particularly it relates to a coating of a hydrolyzed condensate of an organosilicic compound of which coating is superior in resistance to water and various solvents.
2. Description of Prior Arts
Since shaped plastic products have the defect that they are apt to be easily injured on their surfaces, a proposal has been made to form a cured coating of organopolysiloxane on the surfaces of plastic articles in order to prevent them from being injured on their surfaces. Further, various curing catalysts have generally been employed, at the time when the cured film of polyorganosiloxane is formed, and it has been seen that the properties of the resulting coated film are dependent on the kind of curing catalysts employed. Thus, in order to make the physical properties of the coating suitable for these uses, selection of curing catalysts have been considered to be very important. As for the curing catalysts, aliphatic amines, alkali metal salts of lower fatty acids, etc. have been proposed, and the present inventors, too, have previously proposed various metal salts of carboxylic acids (Japanese Patent Application No. 70103/1976), sodium phosphate (Japanese Patent Application No. 71990/1976), and alkali metal salts of inorganic acids (Japanese Patent Application 76191/1976).
However, in the case of coatings of hydrolyzed condensates of organosilicic compounds obtained by employing the conventional curing catalysts such as alkali metal salts of lower fatty acids, sodium phosphate and alkali metal salts of various inorganic acids, a high hardness and a superior resistance to scratching and abrasion may be obtained, but when they are immersed in water for a long time, cloudiness and small spots occur and also the tight adhesion of the coating onto the base product is reduced. Further, if aliphatic amines, various metal salts of carboxylic acids, etc. are employed as the curing catalyst, blistering and peeling occur in a short period of time in contact with organic solvents although high hardness and a resistance to scratching and abrasion are obtained. Thus, those conventional curing catalysts have been inferior in the point of the resistance to solvents and water. It is added that none has been completely satisfactory under severe conditions although other properties might have been superior.